1. Field of the Invention
The present invention relates to a substrate for an inkjet recording head which ejects ink onto a recording surface of a recording medium to perform recording operation, and to an inkjet recording head using the same. An inkjet recording head suitable for applying the present invention has a plurality of ink supply ports which are shaped like long grooves and which lead ink from the opposite surface (backside) of the substrate from the surface where elements for generating energy used to eject ink are arranged, through the substrate to the elements. Furthermore, the inkjet recording head is one which ejects ink in a direction perpendicular to the plane of the substrate in response to the driving of the elements.
2. Description of the Related Art
Inkjet recording heads applied to recording apparatuses which perform recording by imparting ink to recording media such as recording paper include ones which perform ink ejection by various methods. In one method, a heating portion (also called heater) made of a resistive element which generate heat in response to energization is used, and recording is performed by utilizing pressure generated by thermally foaming ink. In this type, a substrate for an inkjet head in which many heating portions, wirings, and the like are arranged at a high density can be manufactured easily and accurately. Accordingly, the finess and speed of recording can be improved. Further, this makes it possible to make more compact the inkjet recording head or a recording apparatus using this.
In one form of an inkjet recording head of the above-described type which utilizes thermal energy, ink is ejected in a direction perpendicular to a main surface of a substrate on which heating portions are arranged. In an inkjet recording head of this form, ink to be ejected is generally supplied from the opposite surface from the above-described main surface through an ink supply port which penetrates a substrate.
FIGS. 1 and 2 illustrate one known example of such an inkjet recording head (hereinafter also simply referred to as a recording head). FIG. 1 is a perspective view illustrating part of a substrate by cutting out part of a member forming ejection openings and the like. FIG. 2 is a plan view illustrating interconnections and the like arranged on a main surface of the substrate of the recording head.
In this type of recording head, as illustrated in FIG. 1, a plurality of heating portions 802 arranged in a staggered pattern on both sides of an ink supply port 803 penetrating the substrate are provided on the main surface of the substrate 805. And in addition, a member for forming ink passages 804 and a plurality of ink ejection openings 801 for ejecting ink which correspond to the plurality of heating portions 802 is placed on the substrate 805. On the substrate 805 illustrated in FIG. 2, in order to selectively drive the plurality of heating portions 802 in accordance with recording data to eject ink, the following wiring, circuit, or the like is provided:                Common power supply lines 902a and 902b connected to a power supply side        The plurality of heating portions 802, heating portion wiring 910 for energizing each heating portion 802, and a driving circuit (hatched portion in the drawing which is formed in a layer lower than the heating portions and a related wiring layer) which includes driving elements such as transistors        Ground (GND)-side common lines 904a and 904b Further, the common lines on the power supply side and the GND side can be electrically connected to the outside of the substrate through electrode pads 903. It should be noted that required interlayer insulating films placed in relation to layers for forming the heating portions, electrode wires, and the driving elements, a protective layer for protection against ink, and the like are not illustrated in the drawing.        
In the inkjet recording head having the above-described configuration, ink is held in a state in which the ink forms a meniscus in the vicinity of each ejection opening 801. The heating portions 802 are selectively driven in accordance with recording data in this state, and the thermal energy generated is utilized to sharply heat and boil the ink on a heat applying surface. Thus, ink can be ejected by the pressure of bubbles generated at this time.
Incidentally, electric energy or power which is applied to the heating portions in order to eject ink is one of important factors which influence the ejection. That is, when the applied electric energy varies, a foaming phenomenon also varies accordingly, and favorable ejection may not be performed. For example, in the case where driving energy applied is small, an ink-boiling phenomenon is prone to become unstable because of an energy shortage. Then, favorable film boiling does not occur. This causes fluctuations in the ejection speed and ejection direction of ink and further causes fluctuations in the ejection amount. These may cause a deterioration in the quality of a recorded image. On the other hand, in the case where the applied driving energy is high, excessive thermal energy imposes mechanical stress on an electrothermal transducer or causes a change in film quality. These may also cause an ejection failure as described above. In extreme cases, the recording head may be broken. Accordingly, it is desirable that an appropriate, substantially constant amount of energy should be applied to each of the plurality of heating portions and that the energies applied to the plurality of heating portions should be substantially equal.
On the other hand, known factors that cause fluctuations in energy applied to each heating portion also include one caused by the fact that the number of heating portions simultaneously driven changes in one recording head. That is, if the number of heating portions simultaneously driven changes depending on recording data or the like, a voltage drop generated changes accordingly. As a result, the driving energy of each heating portion changes.
As one of countermeasures against this problem, heretofore, there has been a configuration disclosed in, for example, Japanese Patent Application Laid-open No. 10-44416 (1998). In this configuration, as illustrated in FIG. 2, each of common wirings between the heating portions 802 and electrode pads and that between the driving elements and the electrode pads is divided into a plurality of portions which correspond to groups of a certain number of heating portions and driving elements. Further, the wiring resistances of the common lines 902a, 902b, 904a, and 904b are approximately equal. This configuration makes it possible to reduce the difference in voltage drop between the case where all heating portions are driven and the case where one heating portion is driven for each group. Further, for each group, the difference in voltage drop between the case where all heating portions in the group are sequentially driven and the case where one heating portion is driven can be eliminated by performing time division driving in units of one heating portion and thus setting the number of heating portions simultaneously driven to one. This makes it possible to always apply constant driving energy to each heating portion.
This configuration is based on reducing voltage drops due to the fact that the length of common wiring for each heating portion differs depending on the position of the heating portion, particularly in the case where one common wiring is provided for all heating portions, among voltage drops caused when the heating portions are driven. Accordingly, in the configuration of Japanese Patent Application Laid-open No. 10-44416 (1998), common wiring widths are made as large as possible to reduce wiring resistances thereof. In addition, the wiring widths, such as widths A and B illustrated in FIG. 2, differ depending on the wiring length to each group. Thus, the wiring resistances are set to be equal.
However, in recent inkjet recording apparatuses, dominating recording heads are ones which have a plurality of ink supply ports in one substrate in order to obtain a high-resolution, high-quality image fast, and into which a plurality of heating portions are integrated at a high density in association with the ink supply ports. Accordingly, the numbers of power supply line terminals, GND line terminals, pulse signal input terminals, and data input terminals continue increasing. Thus, in the case of known connection by individual wiring in units of the certain number of heating portions, the size of a substrate is greatly increased because of the number of electrode pads, and cost is increased. On the other hand, there are demands for the downsizing of recent recording apparatuses. With the demands, recording heads and the like also tend to be downsized. Accordingly, in the case of known connection by individual wiring, it is very difficult to reduce the size of a substrate under the constraint that the size of a recording head cannot be easily increased as described above.